The treatment of injured ligaments and tendons remains a serious clinical problem. Inadequately repaired damage to these structures results in pain, loss of function, and in some cases, subsequent degenerative arthritis. When severely damaged by trauma or disease, fibrous tissue repair is often impossible. Many researchers have suggested the use of replacement structures for such damaged tissue. At this time, however, a completely successful prosthesis for use in a chronic implanation has not been developed.
Difficult fractures of the long bones often require an internal fixation device to maintain stability and alignment during healing. A rigid metallic plate is usually the device of choice, although, ideally, the stiffness of the plate should vary over the course of treatment. During early healing, rigid fixation by plating promotes primary osseous union. Unfortunately, as the healing progresses, a rigid plate can cause cortical bone to atrophy. This stress protection atrophy results in loss of bone mass and remodeling of cortical bone to incompletely mineralized bone. Nor is the remodeling confined to bone directly beneath the plate. It can be observed to a lesser extent in the cortex opposite the plate. The long term result of stress protection is a mechanically inferior bony structure in the region of the plate. Upon removal of the plate, refracture is often a possibility thereby requiring protection and limited activity until sufficient bone strength can be regained.
The use of intermediately stiff plating devices has also been proposed. This compromise solution results in some loss of initial stability with the attendant possibility of non-union. In return there is some long term reduction in stress protection atrophy.
Ideally, the bone fixation plate should be sufficiently strong to promote osseous union at the fracture site and sufficiently flexible to allow at least partial load transference to the fractured bone inasmuch as some loading enhances the healing process.
With respect to the repair of damaged ligaments and tendons it has recently been demonstrated by Jenkins et al, "Induction of Tendon and Ligament Formation by Carbon Implants", J. Bone and Joint Surg., 59-B:53-57, 1977, and Wolter et al, "Ligament Replacement in the Knee Joint with Carbon Fibers Coated with Pyrolytic Carbon", Trans. 3rd Ann. Mtq., Soc. for Biomat., 126, 1977, that ligaments and tendons can be replaced by filamentous carbon implants. New fibrous tissue grows and is gradually aligned, replacing the carbon scaffold which fractures and degrades mechanically.
Alexander et al, "Carbon-Polymer Composites for Tendon and Ligament Replacement", Trans. 4th Ann. Mtg., Soc. for Biomat., 123, 1978, have indicated the need for physically protecting the delicate carbon fibers to avoid difficulty in implantation, premature fracturing in vivo and migration of carbon fibers from the site of surgery.
Kulkarni et al, "Polylactic Acid for Surgical Implant", Arch. Surg., 93, 839-843, 1966, and Cutright et al, "Tissue Reaction to the Biodegradable Polylactic Acid Suture", Oral Surg., 31: 134-139, 1971, have demonstrated the biocompatibility, biodegradability and ease of manufacture of surgical appliances of polylactic acid polymers.
U.S. Pat. Nos. 4,127,902 and 3,971,670 describe structures for in vivo implantation as substitutes for ligaments and tendons comprising a bio-compatible film, a bio-compatible fabric having a weave with no permanent yield in one direction integral with the film and a bio-compatible porous material which promotes the ingrowth of living tissue. The structure is used as a patch for repairing damaged ligaments and tendons and is designed to promote the growth of new ligament and tendon tissue. The patch, however, is intended for permanent implantation to the host animal.
U.S. Pat. No. 3,276,448 discloses the concept of coating a non-absorbable fiber-containing fabric intended for use as a repair structure for damaged tissue with collagen. The collagen is said to serve as a stimulus for new tissue growth in the area of repair.
It has been proposed in U.S. Pat. No. 3,992,725 to utilize carbon fibers as in vivo implantation material due to its ability to foster new tissue growth by virtue of its bio-compatibility. The patent proposes to combine the carbon fibers with polytetrafluoroethylene bonding material to provide a relatively permanent implant material.
U.S. Pat. No. 3,463,158 discloses the use of composites of polyglycolic acid and non-absorbable fibrous material as implants for tissue repair or replacement. The composition is designed such that new tissue growth surrounds the non-absorbable fibrous material.
U.S. Pat. No. 3,893,196 describes a material for fabricating a prosthesis comprising graphite fibers embedded in a coating with a medically inert plastic.
U.S. Pat. No. 3,272,204 discloses an absorbable collagen prosthetic implant reinforced with strands of non-absorbable material.
As is apparent from the aforesaid references, the use of filamentous carbon as an implant material is not unique. Indeed, it has been demonstrated that new fibrous tissue growth is encouraged by the carbon filaments, with the new tissue gradually aligning and replacing the carbon scaffold which fractures and degrades mechanically. However, filamentous carbon is usually produced on a polymer base, often with the addition of polymer sizing agents. These polymers frequently exhibit adverse tissue reactions or are carcinogens; as is polyacrylonitrile, a commonly used base material. It has been suggested to remove the sizing agent with methyl ethyl ketone possibly leaving trace polymer material behind. Complete removal of the sizing and base residue by heating to 4000.degree. F. results in a strong material that is, unfortunately, brittle and sensitive to shear and bending deformations.
In addition, unprotected carbon has been found to break up during implantation and migrate from its implantation area. In some cases, it forms sinus tracks right through the skin.
The mere mechanical reinforcement of the carbon fibers with other materials does not satisfactorily eliminate the migration problem.
It is an object of the invention to provide a composition, surgical article and method for the fabrication of the surgical article and a surgical method for repairing or replacing a part of the body of a human or non-human animal, wherein the said article promotes and provides a scaffold for the growth of new tissue but is substantially non-migratory and bio-absorbable.